Safety blowgun

ABSTRACT

A safety compressed-air blowgun for protecting a user thereof against exposure to dangerously high pressures and wherein a pressure-responsive valve is arranged in series flow relation with a manually operable valve for precluding delivery of air from the blowgun at dangerously high pressures through movement of a pressure-responsive valve member relative to a valve seat in response to balancing of air pressures and in such a manner that the valve member is seated to preclude passage of air when the pressure of air downstream of the pressure-responsive valve is above a predetermined safe pressure.

United States Patent Inventors John E. Bass, Jr.

Charlotte, N.C.; George R. Ferguson, Clover, S.C. Appl. No. 873,205Filed Nov. 3, 1969 Patented Oct. 12, 1971 Assignee G. W. MurphyIndustries, Inc.

Houston, Tex.

SAFETY BLOWGUN 9 Claims, 7 Drawing Figs.

US. Cl 239/526, 137/613, l37/505.25,137/498, 239/571 Int. Cl B05b 1/32Field of Search 137/613, 85, 498, 500, 503, 505, 505.13, 505.25;239/571, 526

References Cited UNITED STATES PATENTS 2,623,331 7 12/1952 (ireening l37/613 3,074,426 1/1963 Billington 137/505.25 3,075,546 1/1963 Roberts137/613 3,269,411 8/1966 Teston 137/613 3,454,041 7/1969 Massonl37/505.25

Primary Examiner-Laverne D. Geiger Assistant Examiner-William B. WrightAttorney-Parrott, Bell, Seltzer, Park & Gibson ABSTRACT: A safetycompressed-air blowgun for protecting a user thereof against exposure todangerously high pressures and wherein a pressure-responsive valve isarranged in series flow relation with a manually operable valve forprecluding delivery of air from the blowgun at dangerously highpressures through movement of a pressure-responsive valve memberrelative to a valve seat in response to balancing of air pressures andin such a manner that the valve member is seated to preclude passage ofair when the pressure of air downstream of the pressure-responsive valveis above a predetermined safe pressure.

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SHEET 2 OF 3 ATTORNEYS JOHN E BASS 3'2 aha GEORGE RFE-musounvfiwflffleZJpgbgfls Jw PATENTEU nmmsn 13,612,406 SHEET 3 OF 3 JoHN E.51x55, Jiaand GEOZGE $2. FERG SON ATTORNEYS INVENTORS:

SAFETY BLOWGUN This invention relates to a safety blowgun and, moreparticularly to means responsive to the pressure at which compressed airis delivered through a blowgun for protecting a user of the blowgunagainst exposure to dangerously high pressure.

Compressed-air blowguns are widely used in industrial applications forcleaning tools and workpieces during industrial operations such asmachining of metals. With ready availability of compressed-air blowguns,such blowguns have also come to be used by workmen to clean dust and thelike from clothing or the workmens bodies. As will be recognized, suchuse of a compressed-air blowgun exposes a user to danger of significantphysical injury where the pressure of air delivered through the blowgunis relatively high. Implementation of recent industrial safetylegislation has recognized the dangers inherent in such use of acompressed-air blowgun by requiring limitation of the air pressuredelivered through a compressedair blowgun.

In attempting compliance with such industrial safety legislation, twoapproaches have heretofore been used. The first of these approaches isto limit the pressure at which compressed air is supplied throughout anindustrial plant to the pressure specified by the industrial safetylegislation. This approach has serious deficiencies in that suchpressures are below those at which most pneumatically operated toolsfunction efficiently and thus this approach causes interference with themore important reasons for distributing compressed air within anindustrial plant. The second approach is the provision of individualpressure regulators to reduce a more generally distributed relativelyhigh line pressure to a specified lower pressure at locations where acompressed-air blowgun is to be used. This latter approach suffers twodeficiencies, one economic and related to the cost of providing arelatively large number of individual pressure regulator devices and theother safety related in that such individual pressure regulators aresubject to readjustment by workers more interested in obtaining a highpressure at a compressed-air blowgun than in compliance with safetystandards.

With the above discussion in mind, it is an object of the presentinvention to ensure that a user of a compressed-air blowgun is protectedagainst the dangers present where excessively high pressure is releasedthrough such a blowgun and further to ensure that compliance withindustrial safety regulations is achieved and maintained in a mostpractical and economical manner. In realizing this object, a blowgunstructure is provided which may be used in conjunction with any normalair pressure distributed in an industrial plant and yet will protect anemployee-user and comply with the requirements set forth in theaforementioned safety regulations. Valve means are incorporated in theblowgun to permit a user manipulating the blowgun to manually controlthe release of air therethrough and further to preclude delivery of airfrom the blowgun at dangerously high pressures. In particular, first andsecond valve means are arranged in series flow for controllingcompressed airflow through the safety blowgun under manual control andin response to air pressures.

It is a further object of the present invention to provide for readyadaptation of previously existing compressed-air blowguns torequirements of limiting pressure pursuant to the aforementionedlegislation. To this end, the present invention contemplates thecombination, with a pneumatic blowgun, of means for protecting the userthereof against exposure to dangerously high pressure. Such protectivemeans preferably takes the fonn of a pressure-responsive valve membermounted and arranged for movement in response to a balancing ofcompressed-air pressure upstream of the valve means, compressed-airpressure downstream of the valve means, ambient atmospheric airpressure, and a biasing force imposed by a resilient means.

Some of the objects and advantages of the invention having been stated,others will appear as the description proceeds, when taken in connectionwith the accompanying drawings, in which:

FIG. 1 is a perspective view of a safety blowgun assembly incorporatingthe present invention;

FIG. 2 is an elevation view, in section, through the blowgun assembly ofFIG. 1;

FIG. 3 is an enlarged elevation view, in section, througha portion ofthe blowgun assembly of FIG. 2;

FIG. 4 is a reduced respective view, in exploded form, illus' tratingcertain of the valve means elements incorporated in the blowgun assemblyof FIGS. 1-3;

FIG. 5 is a view similar to FIG. 2, showing a modified form of safetyblowgun assembly in accordance with the present in vention; FIG. 6 is anexploded perspective view of certain elements incorporated in a valvemeans useful in a combination constructed in accordance with the presentinvention; and

FIG. 7 is an enlarged elevation view, partially in section,

through an assembled valve means of FIG. 6. I {g Referring now moreparticularly to the drawings, it is to noted that the present inventioncontemplates more than one arrangement of elements in achieving a safetyblowgun. assembly and valve accomplishing the objects set forth above.The present discussion will proceed first with reference to aparticularly preferred form for a safety blowgun assembly in accordancewith this invention, with attention to be turned to alternativearrangements at a later point herein. In this connection, it is to benoted that the safety blowgun assembly generally indicated at 10 inFIGS. 1-3 include a blowgun' body 1 l configured for ready manipulationand having a passage 12 therethrough for the flow of compressed air.Preferably, the blowgun body 11 is constructed by a suitable process ofcasting and machining metal, as has heretofore been known in themanufacture of such industrial products. Interposed in the passage 12are first and second valve means for controlling airflow therethrough,with the valve means being arranged in series flow relation such thatair passing through the blowgun body 11 passes in succession through thetwo valve means and closure of either of the two valve means iseffective to prevent release of air through the safety blowgun assembly10.

The first valve means, generally indicated at 20, is a manually operablevalve adapted for actuation by a user manipulating the blowgun body 11.The first valve means 20, elements which are shown in greater detail inFIGS. 3 and4, includes a first valve seat 21 which preferably is fonnedby"a conical shoulder machined from the body 11 of the blowgun, asdescribed more fully hereinafter, and a first valve member 22 movablerelative to the first valve seat 21. The first valve member 22preferably is a generally conically configured plug member seated uponthe extremity of an operating rod 24, which operating rod penetrates thebody 11 of the blowgun and is movable relative thereto for controllingdisplacement of the valve member 22. In order to provide formanipulation of the first valve means by a user of the blowgun 10, anoperating trigger member 25 is provided and is mounted to the body 11 ofthe blowgun for pivotal movement relative thereto. The trigger 25 abutsa lower extremity of the operating rod 24 (FIG. 2) for displacing thesame upon the blowgun body being gripped by a user. The trigger member25 and rod 24 together form an actuation means for displacing the firstvalve member 22 from a seated position upon the first valve seat 21.

The first valve member 22 is resiliently biased toward a seated positionon the first valve seat 21 by a compression spring member 26 receivedwithin the blowgun body 11 and engaging the first valve member 22 (FIGS.3 and 4). The end portion of the spring member 26 remote from the firstvalve member 22 abuts a ring member 21 which is fixed relative to agenerally cylindrical enclosing wall 29. The enclosing wall 29 is formedby an enlarged portion of the passage through the blowgun body 11 (asseen in FIGS. 2 and 3) and serves a number of various functions in thestructure of the present invention. While it is convenient for machiningand for assembly purposes to form the blowgun body 11 with aconfiguration illustrated in FIGS. 1 and 2, and fonn generallycylindrical enclosing wall 29 by drilling transversely into the body 11as there illustrated, it is to be understood that the enclosing wall 29may be provided in other manners as will be pointed out more fullyhereinafter. Similarly, provision may be made for providing a stationaryabutment to be engaged by the spring member 26 through means other thanthe inserted ring member 28.

The enclosing wall 29, in the arrangement to which the presentdiscussion is directed, additionally surrounds elements of a secondvalve means generally indicated at 30, for cooperation therewith. Inparticular, the second valve means 30 includes a guiding member 31having a generally tubular portion of predetermined length with a boretherewith communicating with and forming a portion of the airflowpassage 12 through the blowgun body 11 (FIG. 3). The guiding member 31has a generally cylindrical exterior wall 32 at the tubular portionthereof, for cooperation with other elements of the second valve means30 as pointed out more fully hereinafter. The arrangement of the guidingmember 31 within the enclosing wall 29 is such that the enclosing wall29 surrounds a termination of the guiding member tubular portion and isarranged concentric with the exterior wall 32 thereof. Thus, thecylindrical walls 29 and 32 together define a generally annular volumewithin the body 11 of the blowgun 10.

A generally annular pressure-responsive valve member 35 is interposedbetween the cylindrical walls 29 and 32 and occludes the spacetherebetween (FIG. 3). The valve member 35 has a generally disclike,annular, main body portion 36 having an open space centrally thereof anda flexible skirt portion 38 along the outer circumference thereof. Aflow control portion 39 of the valve member 35 is located centrally ofthe open space and includes a right circular conical surface for seatingin the bore through the guiding member 31 at the termination thereof.The inside diameter of the central opening through the valve member 35is sized for engagement with the generally cylindrical exterior wall ofthe tubular portion of the guiding member 31, while the circumferentialskirt portion 38 has an outside diameter sized for engagement with thegenerally cylindrical enclosing wall 29. The valve member 35 is guidedby this engagement with the cylindrical walls 29, 32 in linear movementalong the guiding member tubular portion and relative to the terminationthereof. With such linear movement, the right circular conical surfaceof the flow control portion of the valve member 35 engages thetermination of the guiding member 31 tubular portion and closes thepassage 12 against airflow therethrough.

With a particular view toward providing protection for a user of theblowgun against exposure to dangerously high pressures, movement of thevalve member 35 results from a balance of a resilient biasing forceacting against the valve member 35 and air pressures acting againstpiston areas thereof. In particular, a spring means such as acompression spring 40 is provided for exerting on the valve member 35 a.force biasing the valve member relative to the termination of thetubular portion of the guiding member 31. Forces which function incooperation with the spring means biasing force arise from the action ofcompressed-air pressure upstream of the termination of the bore throughthe guiding member 31 on an annular piston area of the valve member 35;compressedair pressure downstream of the termination on an annularpiston area; and ambient atmospheric air pressure.

More particularly, ambient atmospheric air pressure is admitted to aninternal chamber defined within the body 11 of the blowgun 10 by apassageway 45 extending from the exterior of the body 11 to theenclosing cylindrical wall 29 (FIGS. 2 and 3). By provision of thepassageway 45, a chamber defined by cooperation of the guiding member31, the upper annular surface area of the valve member 35 and theenclosing wall 29 is maintained at ambient atmospheric air pressure.Thus, the air pressure acting on an area of the valve member 35 definedbetween the cylindrical walls 29, 32 gives rise to a force acting in thesame direction as the biasing force developed by the compression spring40, to resist movement of the valve member 35 toward the seatedposition. Movement of the valve member 35 toward the seated position isadditionally resisted by the application of compressed-air pressureupstream of the termination of the bore through the guiding member 31 toan area of the valve member 35 defined by the flow control portion andequal to the projected area of the flow control portion relative to thebore through the guiding member 31. Finally, compressed-air pressuredownstream of the bore termination acts against an annular piston areadetermined by the inside diameter of the enclosing cylindrical wall 29.It is to be understood that, in the sense used herein, the phraseannular piston areas" refers to both to full circular piston areas aswell as piston areas defined between concentric circular limits, so asto encompass the areas of the valve member 35 described immediatelyabove.

It is further to be understood that forces arising from the airpressures acting on the piston areas of the valve members 35 and fromthe spring means 40 moves the valve member 35 between the seatedposition on the bore termination when the pressure of air flowingthrough the passage 12 downstream of the second valve member 35 exceedsa predetermined safe pressure and an unseated position when suchpressure is below the predetermined safe pressure. More specifically,should a user of the blowgun 10 manipulate the trigger 25 and open thefirst valve means 20 for the delivery of air through the passage 12 ofthe blowgun 10, the balance of forces acting on the second valve member35 normally is such as to open the passageway to the flow of air andresult in delivery of air from the blowgun 10 to whatever end use isdesired by the user. However, should the user manipulate the blowgun 10to position the outlet nozzle therefrom closely adjacent any obstructingsurface such as his skin surface, a back pressure builds up within thepassage 12 downstream of the first and second valve means 20 and 30.Such a buildup of back pressure within the passage 12 acts to increasethe forces tending to seat the second valve member 35 and results inclosure of the passage 12. Desirably, the back pressure within thepassageway 12 at which this action occurs is set with a view tocomplying with regulations promulgated under the industrial safetystatutes mentioned heretofore. As will be understood, the operation ofthe safety blowgun assembly described to this point protects a user byentirely precluding the application of dangerously high pressures to theuser by means of the blowgun assembly.

In assembling the blowgun assembly described to this point, the guidingmember 31 preferably includes means for ensuring sealing of thepassageways and chambers defined thereby against undesirable pressureflows. To this end, aryO-ring seal 41 is provided around a portionthereof which separates the bore through the guiding member 31 from thechamber to which ambient air pressure is applied through the passageway45. Further, a second sealing O-ring 48 (FIGS. 2 and 3) seals theexterior end of the guiding member 31 against possible escape ofcompressed air thereby. In order to ensure the desired flow ofcompressed air thereby. In order to ensure the desired flow ofcompressed air through the passage 12 formed in the body 11 of theblowgun 10, the guiding member 31 is formed with a circumferentialgrooved portion extending therearound for flow of air into the borestherethrough. Advantage is taken of the presence of the circumferentialgroove to permit use of a threaded locking pin 49, which enters throughthe body 11 of the blowgun 10 and secures the guiding member 31 inassembled relation with the body 1 1.

While the discussion to this point with reference to a safety blowgunassembly 10 in which the pressure-responsive valve means 30 ispositioned upstream of the manually operable valve means 20, the presentinvention further contemplates that the series flow arrangement of thevalve means may be reversed. Such a combination is illustrated in FIG.5, wherein a pneumatic blowgun 50 is illustrated. Where structuralelements of the pneumatic blowgun 50 are identical or substantiallysimilar to structural elements of the safety blowgun assembly 10described heretofore, the reference characters applied are the same withthe addition of prime notation. For example, the body 11' of thepneumatic blowgun 50 is generally similar to the body 11 of, the safetyblowgun assembly described heretofore.

Points of distinction between the safety blowgun assembly 10 and thepneumatic blowgun 50 include the provision, in the first valve means ofmeans for limiting the stroke or scope of movement of the first valvemember 22'. By such limitation, control ,over the volume of the airdelivered through the manually operable first valve means 20' may beexercised, providing advantages under some circumstances of use for thepneumatic blowgun 50. Such limitation is obtained by an up wardlyextending pin member 51 which moves relative to an adjustable threadedstop member 52.

Other points of distinction as'to the pneumatic blowgun 50 are found inthe construction and arrangement of the second valve means 20'. In thatvalve means, the generally cylindrical enclosing wall 29' is provided bya threaded barrel member 55. One end of the threaded barrel member 55engages an external thread provided on the body 1 I of the pneumaticblowgun 50, so that the generally cylindrical interior wall 29' of thebarrel member 55 surrounds an end portion of the body 11' formed toprovide the guiding member 31'. The opposite end of the barrel member 55is internally threaded to receive a flow-directing nozzle portion suchas is illustrated in the safety blowgun assembly of FIGS. 1 and 2. Dueto this construction, the spring 40' used in the combination of FIG. 5may be constructed somewhat differently from the spring 40 shown inFIGS. 3 and 4, while the valve member 35' may be constructed preciselyidentically to the valve member 35 used in assembly describedheretofore.

In the combination of FIG. 5, the operation of the pressureresponsivevalve is the same as the function described above with reference to thevalve 30 and the assembly of FIGS. 1-4. That is, the valve member movesto a seated position in response to a rise in back pressure downstreamof the valve, to preclude the application of dangerous pressures to auser of the pneumatic blowgun 50.

The present invention further contemplates that the pressure-regulatingvalve means discussed above with reference to the valves 30 and30' inthe safety blowgun l0 and pneumatic blowgun combination may additionallybe constructed for addition to preexisting blowguns presently in use orfor other pressure-regulating applications. As so constructed, thepressure-regulating valve means permits ready modification of existingequipment in order to comply with safety regulations promulgatedpursuant to the legislation mentioned heretofore. Such apressure-regulating valve means 30" is illustrated in FIGS. 6 and 7,where elements identical or generally similar to elements describedheretofore have been identified by double prime notation. It will benoted that the pressure-regulating valve means 30" includes a barrelmember 50" and a guiding member 31" which cooperate substantially in themanner described above with reference to FIG. 5. In this instance, theguiding member 31 is provided with external threads on both ends, withone set' of threads being engaged by the barrel member and with theother set of threads being sized to replace a discharge nozzle elementnormally secured in the" body of a preexisting blowgun. In order tomodify a preexisting blowgun and obtain the advantages of the presentinvention, it is only necessary to remove a preexisting nozzle memberand insert the pressure-regulating valve means 30" of FIGS. 6 and 7.

In the drawings and specification, there have been set forth preferredembodiments of the invention, and although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation.

What is claimed is: p

1. A safety blowgun for protecting a user against exposure todangerously high pressure comprising:

a blowgun body includinga nozzle portion for directing a blowing streamof air, a handle portion configured for ready gripping in the hand of auser and manipulation thereby, and a passage extending from said handleportion to said nozzle portion for compressed airflow through saidblowgun body,

first valve means in said passage for controlling airflow therethrough,

manually operable trigger means mounted on said blowgun body for manualactuation by a user gripping said handle portion, said trigger meansbeing operatively connected to said first valve means for opening andclosing said first valve means upon manipulation of said trigger means,and

second valve means in said passage in'series flow arrangement with saidfirst valve means and for limiting the pressure at which said blowingstream'of air passes through said nozzle portion, said second valvemeans comprising a second valve seat, a second valve member movablerelative to said second valve seat and having piston areas thereofexposed to compressed-air pressure upstream of said second valve seatand to compressed-air pressure downstream of said second valve seat, andresilient means exerting a force biasing said second valve memberrelative to said second valve seat, the resilient means forcefunctioning with forces arising from said air pressures acting on saidpiston areas of said second valve member for moving said second valvemember between an unseated, flow-continuing position when the pressureof air within said passage downstream of said second valve means isbelow a predetermined safe pressure and a seated, flow} interruptingposition on said second valve seat when the pressure of air within saidpassage downstream of said second valve means is above saidpredetermined safe pressure.

2. An assembly according to claim 1 \vhereinsaid second valve means ispositioned upstream of said first valve means.

3. An assembly according to claim 1 wherein said second valve means ispositioned downstream of said first valve means. 1

4. An assembly according to claim 1 wherein said second valve seat, saidsecond valve member and said resilient means are so arranged andcooperate that said resilient means biases said second valve membertoward said unseated position and force arising from air pressuredownstream of said second valve means acts to urge said second valvemember toward said seated position and in opposition to force arisingfrom air pressure upstream of said second valve means.

5. An assembly according to claim 4 wherein said resilient means biasingsaid second valve member comprises a compression spring having one endengaging said body and the other end engaging said second valve member.

6. An assembly according to claim 4 wherein said second valve meansfurther comprises means defining a pair of concentric, spaced-apartgenerally right circular cylindrical walls and further wherein saidsecond valve member has a generally annular body occluding the spacebetween said concentric cylindrical walls and is guided by engagementtherewith in linear movement relative to said second valve seat, saidsecond valve member further having a centrally located generally conicalprojection for valving engagement with said second valve seat onmovement of said second valve member relative thereto and in continuedengagement with said concentric cylindrical walls.

7. A safety blowgun for protecting a user against exposure todangerously high pressure comprising:

a blowgun body including a nozzle portion for directing a blowing streamof air, a handle portion configured for ready gripping in the hand of auser and manipulation thereby, and a passage extending from said handleportion to said nozzle portion for compressed airflow through saidblowgun body,

first valve means in said passage for controlling airflow therethrough,

manually operable trigger means mounted on said blowgun body for manualactuation by a user gripping said handle portion, said trigger meansbeing operatively connected to said first valve means for opening andclosing said first valve upon manipulation of said trigger means,

a guiding member having a generally tubular portion of predeterminedlength with a bore therethrough forming a portion of said passage andterminating in a second valve seat and having a generally cylindricalexterior wall,

a generally cylindrical enclosing wall surrounding said termination ofsaid guiding member tubular portion and arranged concentric with saidexterior wall thereof and having means defining a passageway forcommunication of the volume defined between said cylindrical walls withthe ambient atmosphere,

a generally annular pressure-responsive second valve member interposedbetween said cylindrical walls and occluding the space therebetween,said second valve member being guided by engagement with saidcylindrical walls in linear movement along said guiding member tubularportion and relative to said termination thereof and having a flowcontrol portion for seating in said bore at said termination and forclosing said passage against airflow therethrough, said second valvemember having annular piston areas thereof exposed to compressed-airpressure upstream of said termination, to compressed-air pressuredownstream of said tennination and to ambient atmospheric air pressure,and

spring means for exerting on said second valve member a force biasingsaid second valve member relative to said termination, said spring meansforce functioning with forces arising from said air pressures acting onsaid piston areas of said second valve member for moving said secondvalve member between a seated position on said termination when thepressure of air flowing through said passage downstream of said secondvalve member exceeds a predetermined safe pressure and an unseatedposition when the pressure of such air is below said predetermined safepressure.

8. The combination of claim 7 wherein said piston area of 9. Thecombination of claim 8 wherein said spring means comprises a coiledcompression spring positioned encircling said guiding member tubularportion and engaging said valve member for urging the same away from thepassage-closing position thereof.

1. A safety blowgun for protecting a user against exposure todangerously high pressure comprising: a blowgun body including a nozzleportion for directing a blowing stream of air, a handle portionconfigured for ready gripping in the hand of a user and manipulationthereby, and a passage extending from said handle portion to said nozzleportion for compressed airflow through said blowgun body, first valvemeans in said passage for controlling airflow therethrough, manuallyoperable trigger means mounted on said blowgun body for manual actuationby a user gripping said handle portion, said trigger means beingoperatively connected to said first valve means for opening and closingsaid first valve means upon manipulation of said trigger means, andsecond valve means in said passage in series flow arrangement with saidfirst valve means and for limiting the pressure at which said blowingstream of air passes through said nozzle portion, said second valvemeans comprising a second valve seat, a second valve member movablerelative to said second valve seat and having piston areas thereofexposed to compressed-air pressure upstream of said second valve seatand to compressed-air pressure downstream of said second valve seat, andresilient means exerting a force biasing said second valve memberrelative to said second valve seat, the resilient means forcefunctioning with forces arising from said air pressures acting on saidpiston areas of said second valve member for moving said second valvemember between an unseated, flow-continuing position when the pressureof air within said passage downstream of said second valve means isbelow a predetermined safe pressure and a seated, flow-interruptingpositiOn on said second valve seat when the pressure of air within saidpassage downstream of said second valve means is above saidpredetermined safe pressure.
 2. An assembly according to claim 1 whereinsaid second valve means is positioned upstream of said first valvemeans.
 3. An assembly according to claim 1 wherein said second valvemeans is positioned downstream of said first valve means.
 4. An assemblyaccording to claim 1 wherein said second valve seat, said second valvemember and said resilient means are so arranged and cooperate that saidresilient means biases said second valve member toward said unseatedposition and force arising from air pressure downstream of said secondvalve means acts to urge said second valve member toward said seatedposition and in opposition to force arising from air pressure upstreamof said second valve means.
 5. An assembly according to claim 4 whereinsaid resilient means biasing said second valve member comprises acompression spring having one end engaging said body and the other endengaging said second valve member.
 6. An assembly according to claim 4wherein said second valve means further comprises means defining a pairof concentric, spaced-apart generally right circular cylindrical wallsand further wherein said second valve member has a generally annularbody occluding the space between said concentric cylindrical walls andis guided by engagement therewith in linear movement relative to saidsecond valve seat, said second valve member further having a centrallylocated generally conical projection for valving engagement with saidsecond valve seat on movement of said second valve member relativethereto and in continued engagement with said concentric cylindricalwalls.
 7. A safety blowgun for protecting a user against exposure todangerously high pressure comprising: a blowgun body including a nozzleportion for directing a blowing stream of air, a handle portionconfigured for ready gripping in the hand of a user and manipulationthereby, and a passage extending from said handle portion to said nozzleportion for compressed airflow through said blowgun body, first valvemeans in said passage for controlling airflow therethrough, manuallyoperable trigger means mounted on said blowgun body for manual actuationby a user gripping said handle portion, said trigger means beingoperatively connected to said first valve means for opening and closingsaid first valve upon manipulation of said trigger means, a guidingmember having a generally tubular portion of predetermined length with abore therethrough forming a portion of said passage and terminating in asecond valve seat and having a generally cylindrical exterior wall, agenerally cylindrical enclosing wall surrounding said termination ofsaid guiding member tubular portion and arranged concentric with saidexterior wall thereof and having means defining a passageway forcommunication of the volume defined between said cylindrical walls withthe ambient atmosphere, a generally annular pressure-responsive secondvalve member interposed between said cylindrical walls and occluding thespace therebetween, said second valve member being guided by engagementwith said cylindrical walls in linear movement along said guiding membertubular portion and relative to said termination thereof and having aflow control portion for seating in said bore at said termination andfor closing said passage against airflow therethrough, said second valvemember having annular piston areas thereof exposed to compressed-airpressure upstream of said termination, to compressed-air pressuredownstream of said termination and to ambient atmospheric air pressure,and spring means for exerting on said second valve member a forcebiasing said second valve member relative to said termination, saidspring means force functioning with forces arising from said airpressures acting on said piston areas of said second valve member formoving Said second valve member between a seated position on saidtermination when the pressure of air flowing through said passagedownstream of said second valve member exceeds a predetermined safepressure and an unseated position when the pressure of such air is belowsaid predetermined safe pressure.
 8. The combination of claim 7 whereinsaid piston area of said valve member which is exposed to ambientatmospheric air pressure is defined by the area bounded by the insidediameter of said enclosing wall and the outside diameter of said guidingmember tubular portion; said piston area exposed to compressed-airpressure upstream of said termination is defined by the area bounded bythe inside diameter of said bore through said guiding member; and saidpiston area exposed to compressed-air pressure downstream of saidtermination is substantially as defined by the area bounded by theinside diameter of said enclosing wall.
 9. The combination of claim 8wherein said spring means comprises a coiled compression springpositioned encircling said guiding member tubular portion and engagingsaid valve member for urging the same away from the passage-closingposition thereof.